In what is believed to be the first study to measure the impact of Uber and other ride-booking services on the U.S. ambulance business, two researchers have concluded that ambulance usage is dropping across the country.

A research paper released Wednesday examined ambulance usage rates in 766 U.S. cities in 43 states as Uber entered their markets from 2013 to 2015.

Co-authors David Slusky, an assistant professor of economics at the University of Kansas, and Dr. Leon Moskatel, an internist at Scripps Mercy Hospital in San Diego, said they believe their study is the first to explain a trend that until now has only been discussed anecdotally.

Comparing ambulance volumes before and after Uber became available in each city, the two men found that the ambulance usage rate dipped significantly.

Slusky said after using different methodologies to obtain the “most conservative” decline in ambulance usage, the researchers calculated the drop to be “at least” 7 percent.

“My guess is it will go up a little bit and stabilize at 10 to 15 percent as Uber continues to expand as an alternative for people,’’ Moskatel said.

Slusky said he and Moskatel are submitting the paper to journals for peer review.

San Francisco-based Uber quickly distanced itself from the notion that hailing an Uber driver is an acceptable substitute for calling an ambulance.

“We’re grateful our service has helped people get to where they’re going when they need it the most,” said company spokesman Andrew Hasbun. “However, it’s important to note that Uber is not a substitute for law enforcement or medical professionals. In the event of any medical emergency, we always encourage people to call 911.”

Moskatel, however, said many patients “tend to be pretty good at assessing their state and how quickly they need to come in and how sick they are.”

But at least one prominent Bay Area emergency room physician disagreed.

Paul Kivela, president of the 37,000-member American College of Emergency Physicians, said he believes that for those low-risk patients who can’t drive themselves to the emergency room, Uber is a good service.

But many people, he said, may not be able to differentiate between a life-threatening emergency and an innocuous medical issue. So, he said, calling 911 is always the safest bet.

“A paramedic has the training and the ability to deliver life-saving care en route,” Kivela said. “Where I really have a hard time is believing an Uber driver is going to attend to you.”

Kivela noted that in addition to his work as an ER doctor at Queen of the Valley Medical Center in Napa, he is also the medical director of an ambulance company in Solano County.

The researchers, however, insisted that ride-booking services such as Uber and San Francisco-based Lyft can sometimes be the best way to get to the hospital in a hurry.

Previous research, Moskatel said, “suggests that a fair number of people are using ambulances to get to the hospital because they simply don’t have another way to get there’’ — particularly those who live in areas with limited taxi service.

And, Slusky added, with health care taking a big chunk out of most people’s budgets, many consumers these days have to weigh a few factors before calling an ambulance.

“They have to think about their health — and what it’s going to cost me,” he said. “And for many of us with high-deductible plans, an ambulance ride would cost thousands of dollars.’’

Slusky added: “If we want to reduce (health care) spending, we have to find ways to do things cheaper — and that’s in all kinds of situations where you don’t need the most expensive resource. We don’t all need to fly first-class all the time.”

Moskatel and Slusky said they focused only on Uber because they needed a broad set of data and the company had been operating for a longer period of time than competing services, allowing the researchers to assess a greater number of locations.

Because Uber was not involved in the study, Moskatel had to painstakingly map all the dates the company entered a certain market, based only on the company’s public announcements.

Ambulance rates were obtained from the National Emergency Medical Services Information System, or NEMSIS, a national repository for emergency medical services data.

Slusky said Salt Lake City-based NEMSIS agreed to run the numbers for each city, but an agreement between NEMSIS and its members prevents any release of information that could be used to identify rates for specific regions at the state, city or ZIP Code level.

In Santa Clara County, Emergency Medical Services director Jackie Lowther said there had been “no significant decrease in volumes in Santa Clara County, other than the usual seasonal variation for this time of year.’’

Travis Kusman, Lowther’s counterpart in Alameda County, did not respond to a request for comment. Nor did officials from Lyft.